Electric arc apparatus



Patented Mar. 16, 1943 ELECTRIC Ano APPARATUS Lorne A. Matheson, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a

corporation of Michigan Application July 24, 1941, Serial No. 403,883

(Cl. S14-33)` 4 Claims.

This invention relates to electric arc apparatus, and in particular refers to an apparatus which provides for control of the width of the are gaps.

In a co-pending application of Matheson and Hunt, Serial No. 243,734, filed December 3, 1938, now U. S. Patent No. 2,263,443, there is described an apparatus for the manufacture of acetylene by the cracking of liquid hydrocarbons in seriesoperated alternating current arcs. The electrode mechanism comprises two fixed electrodes connected to opposite poles of an alternating current source, an electrically conducting rotor mounted between the fixed electrodes and adapted to rotate in synchronism with the alternating voltage, and two electrode arms in series with each other mounted on said rotor in such positions as to be brought into substantially simultaneous arcing relationship with the two xed electrodes by the movement of the rotor. y

In such apparatus there is a tendency during normal operation for the electrodes, usually carbon, to wear or, in some cases, to build up carbon deposits. This leads to continually changing widths of the arc gaps and may result on the one hand in a widening of the arc gap to a point where an arc will not strike or, on the other hand, to a collision of the electrodes. It is, therefore, desirable to provide means for controlling the width of the arc gap.

It is, accordingly, an object of this invention to provide for the more successful operation of series-operated alternating current arcs by controlling the width of the arc gap. It is a further object to provide means for adjusting the width of the arc gaps by advancing and withdrawing the fixed electrodes toward or from the moving electrode arms.

I have now found that the width of an arc gap can be adjusted by moving the fixed electrode inwardly or outwardly according to whether the width of the are gap is increasing or decreasing respectively. I have also provided means for producing this inward and outward motion as, for example, by means of a geared-down reversible motor, the direction of rotation of which is determined by an arc striking or failing to strike. The inward and outward motion of a fixed electrode is thereby made responsive to the width of the arc gap.

The invention, then, consists in means for adjustng the distance of the fixed electrodes from the moving electrode arms in series-operated alternating current arc apparatus, as hereinafter fully described and particularly pointed out in Ithe claims, the vannexed drawing, and the followshaft I9.

ing description, setting Aforth in detail certain means for carrying out the invention, such disclosed means illustrating, however, but one of the various ways in which the principle of the invention may be used.

In the accompanying drawing Fig. 1 is a side View, partly in section, of an electric arc apparatus embodying the principle of the present invention.

Fig. 2 is a wiring diagram of an electrical circuit for use in connection with the apparatus of Fig. 1.

Referring now to the drawing, Fig. l shows a chamber 3 having an inlet port 4 for material to be subjected to the action of the arc and an outlet port 5 for products of the cracking. Fixed electrode mechanisms are inserted through the walls of the chamber 3 and may be inclinedk or horizontal, as illustrated. The fixed electrode mechanisms consist of carbon electrodes 6, 6', held in place by steel shafts 1, 'I'. The steel shafts are inserted through the walls of the reaction chamber through suitable stumng boxes 8, 8', which are insulated from the walls of the reaction chamber by porcelain insulators 9, 9'. Pulleys l0, I9' having threaded portions Il, H are attached to the outer ends of the steel shafts l, 1. Internally threaded collars l2, I2' rigidly supported on the insulators 9, 9' by means of bolts I3, i3 impart an axial motion to the shafts 1, l

-when the pulleys l0, l0 are revolved. Driving .belts I4, I4 connect the pulleys l0, I8 with an additional set of pulleys I5, I5', the latter being driven by reversible motors I6, I 6. The fixed electrodes are connected to opposite poles of a high voltage alternating current source by means of cables i1, l1.

A rotating central electrode mechanism is inserted through the top ofthe reaction chamber 3. This mechanism comprises essentially the electrode proper I8, a shaft I9 for rotating the electrode proper I8, and a motor 20 driving the The motor 20 is insulated from the shaft i9 by a shaft section 2| of insulating material. The shaft i9 'enters the top of the reaction chamber through a suitable stuffing box 22 which is insulated from the chamber walls by a porcelain insulator 23. The electrode proper I8 consists of a conducting disc 24 and two electrode arms 25, 25. The electrode arms may be straight rods or may be L-shaped as illustrated in the drawing.

Fig. 2 lshows a plan View of rthe conducting elements shown in Fig. 1 and, in combination therewith, fthe reversible motors `I 6, -l 6 for ymoving the xed electrodes 6, 6' and control circuits which make the direction of rotation of the reversible motors responsive to the width of the arc gaps. A source of high voltage alternating currentl provides single phase current through the cables |1, |1' to the xed electrodes 6, 6 and three phase current to the motor 20. 'Ihe single phase current ows through the cables |1, |1' to the fixed electrodes 6, 6' and across the electrode gaps between the fixed electrodes 6, 6 and the rotating electrode arms 25, 25'. The single phase circuit contains inductances 26, 26' for controlling the arc and the windings of a power relay 30'. The motor 23 driving the electrode arms 25, 25 is inserted in the three phase current circuit by means of a three phase step-down transformer 21. An excitation circuit 28, containing in series an inductance 29 and the windings of a power relay 30, is connected between the central rotor disc 24 and the cable l1 which leads to the xed electrode 6'. The xed electrode 6' is in a position slightly displaced in the direction of rotation of the electrode arms from that diametrically opposite the llxed electrode 6.

The excitation cicuit 28, since it connects the xed electrode 6 with the moving electrode arm 25 equalizes the potential between these two elements, placing the entire available line potential across the other electrode pair, the

electrode arm 25 and the xed electrode 6. In this manner the entire voltage of the source will be across the xed electrode 6 and the electrode arm 25 when these electrodes have reached their minimum distance of separation and an arc will strike between these electrodes. When this occurs the major voltage drop will be across the inductance 23 because of the relatively lov.r resistance of the newly formed arc, and practically all the line voltage will be imposed on the gap between the rlxed electrode 6 and the electrode arm 25'. The arc then strikes in this gap. During the interval between the striking of the arc in the first gap and the striking of the arc in the second gap further rotation of the central rotor brings the electrode arm 25' to its shortest distance of separation from the xed electrode 6. However, the striking of the arcs in the two electrode gaps will be suiciently close together so as to be practically simultaneous.

Each of the reversible motors |6, I3' is connected to a pair of 110 volt control circuits. Wires 3| and 33 and wires 32 and 33 constitute the pair of control circuits for reversible motor |6. Likewise wires 3|' and 33 and wires 32' and 33' constitute the pair of control circuits for reversible motor I6'. Resistances 31, 31' are placed in the leads 3|, 3|. Current in the wires 3| and 33 causes the reversiblev motor |6 to move the rlxed electrode 6 outwardly whereas current in the wires 32 and 33 causes the motor to move the same electrode inwardly. Likewise, a current in the wires 3|' and 33' causes the reversible motor I6 to move the fixed electrode 6 outwardly whereas a current in the wires 32' and 33' causes the motor to move the same electrode inwardly. Switch 34, which is actuated by the relay 36, allows the current to flow in wire 3| or in wire 32, but not in both. Likewise, the switch 34 allows the current to flow in wire 3| or in wire 32', but not in both. A relay 35, actuated by a liow of current in the wires 3| an-d 33, operates a switch 36 in the current line to the reversible motor I6'.

Thus, according to the preferred embodiment of the invention, the fixed electrodes 6, 6' are moved inwardly and outwardly by an axial motion imparted by the reversible motors I6, I6' via the driving pulleys l5, l5', the belts I4, Il', and the follower pulleys I0, I0'. As long as the arc gap between the fixed electrode 6 and the moving electrode arm 25 is operating, there will be a current in the excitation circuit 28 which will actuate the relay 30 and draw the switch 34 out of its normal position. Current from the volt source will then flow in the wires 3| and 33 and cause the reversible motor I6 to move the xed electrode 6 outwardly. On the other hand, if the gap between the iixed electrode 6 and the electrode arm 25 should become so wide that an arc does not strike, current will cease to flow in the excitation circuit 28, the relay 30 will no longer be actuated, and the switch 34 will return to its normal position, i. e., contacting the wire 32. Current then flows in wires 32 and 33, causing the reversible motor I6 to move the xed electrode 6 inwardly.

Likewise, when the arc gap between the xed electrode 6' and the electrode arm 25 is Operating, the current in the cable l1' will actuate the relay 30 and draw the switch 34 out of its normal position. Current from the 110 volt source then iiows through vwires 3| and 33', causing the reversible motor` I6' to move the fixed electrode 6 outwardly. When the arc gap between the fixed electrode 6 and the electrode arm 25' becomes so wide that an arc does not strike, current will not iiow in the cable |1, the relay 30' will no longer be actuated, and the switch 34' will return to its normal position, i. e. contacting the wire 32'. Current from the 110 volt source now fiows in the wires 32' and 33', causing the reversible motor I6 to drive the fixed electrode 6' inwardly.

The relative speeds ol the inward and outward motions of a xed electrode may be adjusted by suitable resistances. As illustrated, the resistances 31, 31' in the wires 3|, 3|' would cause the outward motion to be relatively slower.

In View of the fact that the failure of an arc to strike in the gap between the xed electrode 6 and the electrode arm 25 will cause a failure of the arc to strike in the gap between the fixed electrode 6 and the electrode arm 25', it is desirable that the control circuits operating the reversible motor I6' be open while the fixed electrode 6 is being moved inwardly. Otherwise, a failure of an arc to strike in the gap between the fixed electrode 6 and the electrode arm 25 will cause the fixed electrode 6' to be moved inwardly regardless of how close this electrode is to an electrode arm. This temporary opening of the control circuit to the reversible motor |6' is done at switch 36, which is operated by the relay 35. The switch is open when there is no ilow of current in the wires 3| and 33, that is, when the electrode arm 6 is being run inwardly.

I have found that the operation of series-operated alternating current arc apparatus in accordance with the principles of my invention has resultecl in several important advantages. ,Failures oi the arcs to strike, resulting in decreased electrical efficiency, and collisions of the electrodes, resulting in mechanical abrasion or complete destruction of the electrodes, have been considerably reduced. f

I claim:

l. In an electric arc apparatus, in combination with a source of alternating current: an electrically conducting rotor adapted to rotate in synchronism with the alternating voltage; two .electrode arms in series with each other mounted oppositely on said rotor; two fixed electrodes of polarity opposite one another mounted in such riti-on as to be brought into substantially siu ies-us arcing relationship with the electrode las by the movement oi the rotor, one oi said electrodes being in a position displaced slightly in the direction of rotation from that diametrically opposite the other xed electrode; eacitat" circuit between the rotor and the displaced d electrode, said excitation circuit having in series an impedance and a relay; a reversible motor for each fixed electrode adapted to move the fixed electrode inwardly when rotating in one direction and outwardly when rotating in the other direction; a pair of control circuits for each reversible motor adapted to control the direction of rotation ci said motor; a relay for each oi control circuits, one oi said relays being the aforementioned relay of the excitation circuit and the other being in series with the displaced nxed electrode; and a switch for each re lay, actuated by said relay, and adapted to open one circuit of a pair of control circuits and to close the other of the pair.

2. In an electric arc apparatus, in combination with a source of alternating current: an electrically conducting rotor adapted to rotate in synchronism with the alternating voltage; two electrode arms in series with each other mounted oppositely on said rotor; two xed electrodes of polarity opposite one another mounted in such position as to be brought into substantially simultaneous arcing relationship with the electrode arms by the movement of the rotor, one of said xed electrodes being in a position displaced slightly in the direction of rotation from that diametrically opposite the other fixed electrode; an excitation circuit between the rotor and the displaced fixed electrode, said excitation oircuit having in series an impedance and a relay; a reversible motor for each xed electrode adapted to move the ixed electrode inwardly when rotating in one direction and outwardly when rotating in the other direction; and means for stopping the motor controlling the displaced xed electrode when the other fixed electrode is being moved inwardly.

3. In an electric arc apparatus, in combina tion with a source of alternating current: two lixed electrodes connected to opposite poles of the current source; an electrically conducting rotor mounted between the iixed electrodes and means ier rotating the same in'synchronism with the alternating Voltage; two electrode arms in series with each other mounted on the rotor in such position as to be brought into substantially simultaneous arcing relationship with the fixed electrode by the movement of the rotor; and means responsive to the current flowing in each arc gap for moving the corresponding ixed electrode outwardly at a slow rate when current is flowing in the gap and inwardly at a rapid rate when no current is flowing in the gap.

4. In an electric arc apparatus, in combination with as source oi alternating current: an electrically conducting rotor having two electrode arms mounted oppositely thereon in series With each other, and means for rotating the rotor in synchronism with the alternating voltage; two xed electrodes connected to opposite poles of the current source and mounted in such position as to be brought into substantially simultaneous arcing relationship with the electrode arms by the movement of the rotor, one of said xed electrodesl being in a position displaced slightly in the direction of rotation from that opposite `the other xed electrode; an excitation circuit containing impedance connected between the rotor and the displaced fixed electrode; a first means responsive to the current in the excitation circuit for moving the non-displaced fixed electrode outwardly when such current is flowing and inwardly when no such current is owing; a second means responsive to the current flowing to the displaced electrode for moving the same outwardly when such current is flowing and inwardly when no such current is flowing; and means for rendering said second means inoperative to move the displaced electrode inwardly when the said first means is moving the non-displaced electrode inwardly.

LORNE A. MATHESON. 

